diff options
Diffstat (limited to 'math/modSqrt.cpp')
| -rw-r--r-- | math/modSqrt.cpp | 23 |
1 files changed, 0 insertions, 23 deletions
diff --git a/math/modSqrt.cpp b/math/modSqrt.cpp deleted file mode 100644 index 367c6c7..0000000 --- a/math/modSqrt.cpp +++ /dev/null @@ -1,23 +0,0 @@ -ll sqrtMod(ll a, ll p) { - assert(powMod(a, (p + 1)/2, p) == 1); //a ist ein quadrat mod p? - if (p % 4 == 3) return powMod(a, (p + 1)/2, p); - if (p % 8 == 5) return powMod(a, (p + 3)/8, p); - ll s = p - 1; - ll r = 0; - while (s % 2 == 0) s /= 2, r++; - ll n = 2; - while (powMod(n, (p - 1)/2, p) != p - 1) n++; - ll x = powMod(a, (s + 1)/2, p); - ll b = powMod(a, s, p); - ll g = powMod(n, s, p); - while (true) { - ll t = b; - ll m = 0; - for (;m < r && t != 1; m++) t = (t * t) % p; - if (t == 1) return x; - ll gs = powMod(g, 1ll << (r - m - 1), p); - g = (gs * gs) % p; - x = (x * gs) % p; - b = (b * g) % p; - r = m; -}} |